@drlaurenhoward I edited an article recently for @thePeerJ in which the authors reported the visual angle for a touchscreen study with non-restrained primates, which sounds similar to your protocol/needs (see Apparatus section) - the authors may be able to help https://t.co/8iE1lXR1se
Don't stop thinking chimps are assholes though. When they put a mother and child in this scenario, the mum was way more selfish than the kid.
Paper: https://t.co/xaGWhvYO08 https://t.co/ABjQBLfJ5M